1. Field of the Invention
The present invention generally relates to an image display apparatus connected to a computer and the like. The present invention is directed to a control operation of heater-consumed electric power of a CRT (cathode-ray tube) display apparatus equipped with a power management function capable of reducing unnecessary power consumption, and also another control operation of rising time of a screen of this CRT display apparatus.
2. Description of the Related Art
In general, image display apparatuses own power management functions capable of saving power consumption thereof. As one of these power management functions, as indicated in FIG. 18, the DPMS (Display Power Management System) of VESA (Video Electronics Standard Association) has been proposed. This DPMS is capable of saving power consumption in such a manner that a use state requested by a computer is detected by checking as to whether or not a sync signal is present, and while electric power consumed in an image display apparatus is reduced in a step manner, desirable reduced power consumption can be realized.
Also, in response to the use state requested by the computer, which is detected by checking as to whether or not this sync signal is present, the image display apparatus is brought into a pause state (suspend mode) under which recovery time (image appearing time) is defined, and also a power-OFF state (power-OFF mode) under which recovery time is not defined. Moreover, the power consumption of the respective states is separately defined based upon the Energy Star Program of U.S. Environment Protection Department and the Swedish National Board for Industrial and Technical Development (in general, referred to as a xe2x80x9cTCOxe2x80x9d).
In a conventional image display apparatus shown in FIG. 19, various sorts of power reducing modes are determined based upon the above-explained standards by combining signals with each other as to whether or not a horizontal sync signal, a vertical sync signal, and a picture signal are present, which are supplied from a computer and the like. In this conventional image display apparatus, several sorts of power reducing operations are carried out.
FIG. 19 is a schematic block diagram for indicating an internal arrangement of a conventional image display apparatus. In this drawing, reference numeral 1 designates a signal generating apparatus such as a computer, reference numeral 2 designates an image display apparatus, and reference numeral 3 designates a power save mode detecting section for detecting a use state requested by the signal generating apparatus 1 by checking as to whether or not the sync signal sent from the signal generation apparatus 1 is present, and for setting a power save mode in response to this detected use state. Also, reference numeral 11 designates a heater ON/OFF control unit for controlling a heater-power-supplying control section 6 (will be discussed later) in response to the detection signal detected from the power save mode detecting section 3 so as to turn ON/OFF heater electric power. Reference numeral 5 designates a power supplying section for supplying the electric power to the heater. Reference numeral 6 designates a heater-power-supplying control section for controlling the heater electric power entered from the power supplying section 5 in response to the ON/OFF control signal supplied from the heater ON/OFF control unit 11, and reference numeral 7 designates a CRT for displaying thereon an image by receiving the heater electric power supplied from the heater-power-supplying control section 6, and for containing a heater 71.
Next, operations of the conventional image display apparatus 2 will now be explained. The conventional image display apparatus 2 performs the power management operation in accordance with the use state requested by the computer by detecting a power-save-requesting signal (for example, checking as to whether or not sync signal is present) sent from the signal generating apparatus 1. In particular, when the power OFF mode is set in which the recovery time (namely, time duration defined until an image appears on image display apparatus 2) from the execution of the power management operation is not restricted, supplying of the electric power to the CRT heater 71 is stopped. At this time, an OFF signal is supplied from the heater ON/OFF control unit 11 to the heater-power-supplying control section 6. At this time, while a resistor 616 is used, such a lower voltage than the heater voltage during the normal display operation is applied to the heater 71 so as to shorten the rising time of the screen.
On the other hand, when the normal display mode, the stand-by mode, and the suspend mode are set, the ON signal is outputted from the heater ON/OFF control unit 11. This ON signal may turn ON the NPN transistor 61 of the heater-power-supplying control section 6, so that the base current of the PNP transistor 62 may flow to turn ON this PNP transistor 62. As a result, the voltage drvied from the power supply section 5 is applied via the PNP transistor 62 to the heater 71 of the CRT 7.
FIG. 20 represents variations in the heater voltage before/after the power save mode is released in the conventional preheat type image display apparatus 2. When the power save mode is selected, the voltage lower then the heater voltage in the normal display mode is applied to the heater within such a range defined by the allowable power consumption so as to preheat this heater to a certain warning temperature, so that the rising time of the screen may be shortened. The optimum heater voltage is applied to the heater immediately after the power save mode is released.
Also, Japanese Patent Unexamined Publication No. Hei. 3-48282 describes another conventional image display apparatus operated as follows: That is, in the power save mode, while the temperature of the heater is measured by employing the temperature sensor, the electric power is supplied to this heater in such a case that the measured temperature is lowered over a predetermined temperature range. Thus, since the temperature of the heater is increased, the temperature of the heater is controlled within a constant temperature range lower than the heater temperature in the normal display mode. This conventional system is featured by that while the heater voltage is ON/OFF-controlled, the ON/OFF-controlled heater voltage is applied in a discontinuous mode.
Since the conventional image display apparatuses are constructed of the above-described arrangements, there are the below-mentioned problems.
As the circuit for reducing the electric power in the power-OFF mode, there is only such an ON/OFF circuit for controlling the supply of the heater voltage to the CRT heater. Therefore, both the power consumption in the power-OFF mode and also the recovery time from the power-OFF mode cannot be freely set by the user. Also, there is another problem that lengthy time is required until the image appears on the screen.
Furthermore, Japanese Patent Unexamined Publication No. Hei. 3-48282 discloses that the control operation is carried out while observing the temperature of the CRT heater. However, the temperature of the heater would be changed with a certain temperature range, depending upon the manufacturing precision of the sensor, so that the recovery time cannot become constant. Also, there is another problem that since the heater supply power in the power save mode must be increased in order to shorten the recovery time, the power consumption would be increased.
The present invention has been made to solve the above-described problems, and therefore, has an object to provide such an image display apparatus. That is, based upon both present power consumption in a power save mode and preset screen rising time when the power save mode is released, a calculation is made of optimum heater voltages and also optimum heater voltage application time in the respective modes. Then, an effective value (root-mean-square value) of a signal entered into the heater is controlled based upon the calculation result. More specifically, when the power save mode is released, this effective value is controlled in such a manner that this effective value may become a higher voltage than the optimum heater voltage in the normal display mode, or at least the same voltage as this heater voltage. As a consequence, both the power consumption in the power save mode and the screen rising time when the power save mode is released can be freely controlled.
In order to achieve the above object, according to the invention, there is provided an image display apparatus comprising: power save mode detecting means for detecting a power-save request or a power-save release; power consumption/image-appearing-time control means for controlling both power consumed in a power save mode and rising time of a screen when the power save mode is released; power supplying means for supplying electric power to a heater of a display unit on which an image is displayed; and heater-power-supplying control means for controlling the electric power supplied from the power supplying means based upon a control signal outputted from the power consumption/image-appearing-time control means so as to supply predetermined electric power to the heater of the display unit.
Further, according to the invention, there is provided a method for controlling an image display apparatus, comprising: a setting step for setting both a power saving amount and rising time of a screen; a power-save detecting step for detecting either a power-save request or a power-save release; a calculating step for calculating a value of a first voltage applied to a heater in a power save mode, a value of a second voltage applied to the heater when the power save mode is released and application time of the first and second voltages based upon the set values; a control signal converting step for outputting a control signal based upon the first voltage value, the second voltage value, and the application time; and a heater-power-supplying control step for supplying predetermined electric power to the heater in response to the control signal.